This invention relates to a process for the heat-treatment of fine-grained material, particularly cement raw material, which is preheated by hot gases in a multistage cyclone preheater, subsequently deacidified to a large extent by additional fuel in a precalcination zone and, finally, calcined to completion in a revolving tubular kiln, the supply of fuel to the precalcination zone being automatically regulated in normal operation in dependence upon a gas temperature of the cyclone preheater in such a way that, in the event of a reduction in this gas temperature, the supply of fuel is increased and vice versa.
In the heat-treatment of fined-grained material, particularly cement raw material, it has proved to be favorable for reasons associated with the plant used to carry out a large part of the calcination of the material outside the revolving tubular kiln in a precalcination zone which forms the lowermost part of the preheater or the transition between the cyclone preheater and the revolving tubular kiln. See, for example, German Auslegeschrifts Nos. 2,324,265 and 2,611,239. Since this calcination (removal of the CO.sub.2 from the raw material) is a highly endothermic process, fuel has to be additionally supplied to the precalcination zone through which the exhaust gases of the revolving tubular kiln and/or cooler air flow(s).
Hitherto, this supply of fuel to the precalcination zone has normally been regulated in dependence upon the exhaust gas temperature of the precalcination zone in such a way that, in the event of a reduction in this gas temperature, the fuel supply is increased and vice versa. In this way, it is possible in normal operation to obtain optimal fuel conditions in the precalcination zone, even in the event of fluctuations in the input of material.
However, closer investigations have shown that this known method of regulation fails when certain types of irregularities or disturbances arise. If, for example, the fuel supplied is not completely burnt in the precalcination zone (for example through disturbances in the air supply), there is a reduction in the exhaust gas temperature of the precalcination zone which initiates the adjustment whereby the supply of fuel is increased. The disturbance in question is further increased in this way.
Accordingly, an object of the present invention is to provide a process of the kind referred to such that, not only in normal operation, but also in the event of the most important types of disturbances in practice, the amount of fuel supplied is rapidly adapted to the particular circumstances prevailing.